


Angelic Instincts

by GayApril16



Category: Supernatural
Genre: Ambiguous/Open Ending, Angels are Weird (Supernatural), Cas kinda acts like a cat, Cas wants Dean, Castiel/Dean Winchester First Kiss, Cuddling & Snuggling, Destiel - Freeform, How Do I Tag, Hurt Castiel (Supernatural), I might add more but probably not, Kinda, Light Reading, M/M, No Plot/Plotless, No Smut, Why Did I Write This?, but not a ton, it's cute, some fluff?
Language: English
Status: Completed
Published: 2020-05-15
Updated: 2020-05-15
Packaged: 2021-03-03 05:55:35
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,114
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24190018
Author URL: https://archiveofourown.org/users/GayApril16/pseuds/GayApril16
Summary: Every few millenia, an angel will go through a simple, natural, effortless growing process. Cas' process just began again—the problem is, it was never meant to happen in a vessel. Or on Earth. Or with damaged grace. Needless to say, there's a series of odd side effects that seriously affect Cas.
Relationships: Castiel & Sam Winchester, Castiel/Dean Winchester
Comments: 4
Kudos: 84





	Angelic Instincts

**Author's Note:**

> Not my best work but it's fun to write so enjoy  
> :)

It started as an itch, a phantom irritation between Cas’ shoulder blades. At first Cas barely noticed it, but within a few hours it’s all Cas could do not to squirm. Scratching didn’t alleviate it in the slightest. Cas sat ramrod-straight in his chair, his hands locked into a death grip on the book he’s—theoretically—reading. Sam is sitting across the table from him, researching on his laptop with a half-dozen books scattered around him in case he needs to reference something. Dean had left on a supply run a while back, and Cas figured he would be home soon.

It was only after Cas reread a page for the third time and still didn’t have a clue what it said did he finally admit to himself that something was wrong. Not that he’d show it, of course. The change in his grace was familiar. A _shift_ of sorts—perfectly normal. But the itching that was plaguing his back? Definitely _not._ Especially since the source of the irritation seemed to be his grace.

Cas closed the book with a _thud_ , digging the heels of his palms into his eyes in the irrational hope that it would somehow help.

The clicks of Sam’s typing stopped. “Cas, are you okay?”

Cas ran his hands down his face as the itching continued to dig into him. He sighed. “No, not really, but I’ll be fine.”

Sam closed his laptop with a snap. “Cas. What’s wrong?”

Cas pursed his lips. “I’m fi—” Almost as if in objection to Cas’ words, the itching turned into white-hot needles of pain, making Cas cut off with a strangled-sounding hiss. His whole body tensed, his shoulders aching as they hunched. Cas squeezed his eyes shut as a wave of dizziness made his vision swirl unpleasantly. 

“Cas!” 

Cas cracked open his eyes to find that Sam was now kneeling next to him, one hand on Cas’ shoulder. 

“You’re obviously _not_ fine. _What’s going on?_ ” 

Cas shook his head as the last of the dizziness faded. “It’s not—there’s nothing you can do,” he warned.

“So you know what’s going on?” Sam paused, then something seemed to click in his mind. “It’s an angel thing, isn’t it.” It was a statement, not a question.

Cas gave a sharp nod, then pushed himself to his feet. Sam scrambled up next to him as Cas wavered. Cas clenched his jaw, focusing on his breathing. Sam reached out to steady him but he jerked away.

“I’m _fine_ ,” he growled. His back may be throbbing with pain, but other than that, he felt normal.

Sam gave him a face that made Cas shrink back a little.

For a brief moment Cas closed his eyes, considering, then made up his mind. “Every few millennia, angels go through a . . . _process_ ,” he said, choosing his words carefully. “It’s hard to explain in human terms what it’s for, but during the process an angel is at their most vulnerable. The process itself isn’t painful or dangerous—it’s actually necessary to our health—but the change—the _shift_ —that happens in our grace for the process to take place leaves us incapable to defend ourselves.”

“It doesn’t _look_ like it's painless,” Sam deadpanned.

“It’s not meant to be done in a vessel. Or on earth. Or probably with damaged grace. But I don’t really have a choice.” Cas’ back flared with pain and he bit his tongue so as to not cry out. He wrapped his arms around himself, though he wasn’t sure what the motion would accomplish.

“So you’re what—having side effects?” Sam asked. Concern was written all over his face.

Cas took a shaky breath. “I don’t know what’s happening,” he mumbled. Admitting it somehow made him feel smaller, and fear started twisting its way into his gut. It wasn’t a pleasant addition to the pain.

Sam exhaled. “Right.” 

Silence fell for a few moments. Cas swallowed dryly as a wave of pain rippled through him. 

“Would sleeping help?” Sam asked.

Cas blinked at him. “I . . . don’t know.” 

“Right.” Sam ran a hand down his face. “Why don’t you try to go get some rest. I’m gonna see if there’s anything that we have that might help.”

“Sam—” Cas started.

“I know, I know,” Sam said, holding his hands up in mock surrender. “It’s not likely. But I’m going to at least check. And I’ll tell Dean what’s happening as soon as he gets back.”

Cas’ stomach did a funny sort of flip at the mention of Dean’s name and he winced. Sam was already making a beeline for the catalog room, so Cas made his way to his bedroom.

Cas was still twisting his way through the hallways when a sort of pressure started building in his throat, sourced from the pain in his back. Neither breathing nor speaking eased it—rather, it kept building. By the time Cas half-slammed his bedroom door, the pressure was painful enough to make his eyes water. He rubbed at them, dashing away tears as he breathed heavily—then the pressure released. A pained sort of keening noise ripped from Cas’ throat, loud and sharp. Cas felt the sound reverberate through his bones, through his _grace_ —and it _did_ something. His grace twisted, changed, spreading a fire that tore through his body. He collapsed to the ground, panicking but unable to do anything as the sensation overwhelmed him, filled him. It short-circuited his thoughts; his grace began to pulse. The pounding roared through him, and Cas could feel himself _change_. 

After what felt like an eternity, his grace settled. The pain died, replaced by an odd sort of buzz that filled Cas’ body. The buzz felt almost sickly warm, tingling underneath his skin in a way that was reminiscent of what Sam and Dean called “pins and needles” after a limb regained circulation. Cas could breathe again, and carefully he relaxed, pushing himself out of the fetal position. He climbed to his feet, stumbling into his bathroom and fumbling for the light.

He leaned against the sink, staring at himself in the mirror. He didn’t _look_ much different. Blue eyes, rough stubble—he just looked even more disheveled than usual. His hair was a disaster, and his clothes were rumpled—shirt untucked, tie askew, his coat cinched oddly in a few places—but otherwise he looked fine. 

The buzzing under his skin hadn’t subsided, and Cas didn’t know what to make of it. It was uncomfortable but not too distracting, and the pain in his back had dulled to a gentle ache. All in all, he could effectively ignore the sensations—though it didn’t make them go away. The buzzing filled every inch of him—from his scalp to his fingertips to around his ribs and down his legs. 

Cas flexed his hands, straightening his fingers. They trembled a bit because of being clenched so long, but with a few seconds of focus Cas was able to get them to still.

Something twisted in Cas’ stomach, sharp and dull at the same time. Cas grimaced, recognizing the sensation from when he was human: hunger.

*****

Nearly an hour later, Cas was sitting at the kitchen table, trying not to make a mess as he practically devoured a PB&J. He could actually taste it, which was nice, if a bit worrying.

“Oh, wow.”

Cas paused, looking up to see Dean standing in the doorway, a case of beer in one hand. He arched an eyebrow in amusement, then stepped into the room, setting the beer on the counter.

“Hungry?” Dean asked in a tone that Cas took to be teasing. Cas didn’t dignify his question with a response, instead taking another bite.

Dean settled down across from him. “How many have you had?” he asked lightly.

Cas swallowed. “This makes nine.”

Dean barked out a laugh, carding a hand through his hair. After a moment he said, “So, another ‘side effect’?”

Cas paused. “I see you’ve talked to Sam.” He watched Dean carefully, gaging his reaction.

“Yeah. Are you okay?”

Cas looked down. “I honestly don’t know. This isn’t . . . normal. Something’s _happening_ to me.”

“ _Happening?_ As in?”

“I’m not sure.”

Silence fell. Cas finished off his sandwich to find that his appetite was finally satisfied, so he started cleaning up the relatively small mess he had made. Dean just watched him, his bright green eyes tracking Cas’ movements.

As Cas finished cleaning, Sam came in. 

“I found a case—accidentally, actually, I was just watching the news,” he said, directing it to no one in specific. “It’s not too far from here.”

“Really?” Dean asked, sounding interested as he perked up a little. “What’re we looking at?”

“Vamp nest, most likely.”

There was a pause, and after a moment Cas realized that they were both looking at him. They didn’t know if he should be benched or not.

“I should stay here,” he clarified, even though the thought of staying behind made him wince a bit. “What’s the phrase—better to be safe than sorry?”

The corner of Sam’s mouth quirked. “Yeah, that’s the right one.”

“You sure you’re going to be okay, Cas? We can put someone else on it if you need us to,” Dean said. He was trying to hide it, but he was worried. Cas could see it in his eyes.

“I’ll be fine,” he blustered, trying to hide his nerves. He actually had no idea—and that terrified him. The buzzing under his skin seemed to shift. “You two go handle it.”

Sam and Dean glanced at each other, and some sort of understanding that Cas couldn’t read passed between them.

“We’ll only be gone a couple of days,” Dean said. “Make sure to call us if _anything_ happens. Alright?”

Cas nodded, not trusting himself to speak.

*****

The first three days spent alone in the bunker were rather uneventful. Cas watched a substantial amount of TV in Sam’s room, careful to keep things neat, as well as read bits and pieces of a few books, but mostly he wandered the bunker, feeling restless. He still wasn’t used to the unnatural sensation that filled his body. He supposed he should be grateful, at least, that so far the only large “effect” that he felt from whatever was going on was periodic bursts of intense hunger, but he was still on edge. Dean had called once, as had Sam, keeping him updated on how the hunt was going.

It was the fourth day—the day Dean and Sam were due back—when Cas went haywire.

It started when Cas woke up. He’d apparently drifted to sleep on Sam’s bed, the TV still running, and the first thing that he noticed when he regained consciousness was that he was _insanely_ hot. He quickly stripped off his coat, the suit jacket and his button-down without a thought, piling them in the ground.

He noticed his hunger next. It was sharper than anything he’d felt before, and he ended up devouring the majority of the food they had to satisfy it.

After that he made his way to the library. He wasn’t really sure what he was doing at this point. He was barely thinking, instead reacting to whatever impulse ran through him. 

He slumped down at one of the tables, his bare arms sprawling across the smooth surface. His mind wandered, but he wasn’t thinking like how he usually would—with words—but with various memories and images that streamed through his mind as he noted the emotions that were attached.

He came across a particular series of memories and made a low keening noise. He climbed onto the table, curling into a ball as the buzzing under his skin shivered with _need_ . It hurt, like how it had hurt when he hadn’t breathed for too long as a human; burning, _aching_. 

He keened again. The need was spreading, twisting into his muscles, his grace.

A sharp ringing sound startled Cas and he jerked, nearly falling off the table. His brain was still operating enough to understand what the sound was, though, so he slipped his cell phone out of his pocket. For a long moment he stared at the words on the screen as it continued to ring, and something in his mind clicked. He blinked, thinking normally again, and quickly answered the phone.

“Cas?” Sam’s voice came through. Cas could head the Impala’s engine in the background.

“Sam,” Cas replied. His voice sounded _wrong_ —thick and broken—and he winced.

Evidently Sam noticed too. “Cas, are you okay?”

“I—” Cas pressed a hand to his forehead. The need he’d been feeling was still rolling through him, burning, but there were other things too, stronger now that he wasn’t giving into them. Impulses, desires—each almost overwhelming.

“Cas?” Sam called, now sounding more than a bit worried. There was a mixture of sounds, which proved to be Dean grabbing the phone.

“ _Cas_ ,” Dean barked.

As soon as Cas heard Dean’s voice another loud keen burst from him, his need surging as he doubled over. Cas slapped a hand across his mouth.

“What the— _Cas_ —”

“I’m sorry,” Cas blurted, removing his hand. “It’s—I can’t—”

“Cas, what’s wrong?” Dean asked urgently, though he sounded like he was trying to stay calm, probably for Cas’ sake.

Cas swallowed. “I—” He wrapped his arms around himself, still sitting on the table. “They’re _inside_ me.”

A pause. “What are?”

“Impulses, urges—I can’t control them,” Cas practically cried. “I can’t—I can’t fight them, they’re too strong, and I’m—” He keened again, and this time the noise made his throat hurt. He tried to cut it off but couldn’t, and had to wait for the noise to stop on its own. “I can’t control myself,” he finally gasped.

Dean let out a string of curses. “We’re only a few hours away, which is what we called to let you know. Hang on.”

The line went dead, and Cas dropped his phone. After a few moments an impulse ran through him, and before he knew what he was doing he was moving, kicking books and lamps off to the floor until he was the only thing left on the table. One of Dean’s jackets was folded over the back of a chair and he snagged it, twisting it in his hands as he curled around himself again. The buzzing twitched, and a wave of exhaustion washed through him. Within seconds, he was asleep.

*****

When he woke up again, his mind was back in that state of non-thinking, reacting purely on his impulses. He blinked at the noises that were echoing out of the halls, then twisted off the table, curling into a ball as he pressed himself against the legs of one of the chairs.

Which was how Sam and Dean found him, bare chested and breathing hard. Dean knelt down in front of him, reaching out. Cas swatted the hand away, then everything in his body surged as he realized he was looking at blonde hair and green eyes.

Within a second he was wrapped around Dean, keening in his shoulder as the painful ache that filled him smoothed away. Dean grunted from the impact, carefully wrapping his arms around Cas after a moment’s hesitation. Cas breathed deep, taking in Dean’s scent as he pressed himself against him. His keening gradually turned into a sort of rumbling, and he relaxed, melting against Dean as warmth ran through his buzz.

Eventually Cas’ mind clicked, and he felt heat redden his cheeks as he buried his face deeper into Dean’s shoulder. The rumbling sound he was making died away, and finally he managed to mumble, “I’m sorry. I can’t—”

“Can’t control it, yeah,” Dean said softly. It was then that Cas actively realized that Dean was holding him, one of his hands gently rubbing circles on Cas’ back. “It’s okay,” Dean added.

They sat there in silence for several minutes, and Cas found he couldn’t let go. After a bit the deep rumbling started in Cas’ chest again.

Dean chuckled. “You sound like a cat.”

“Hey,” Cas protested. It hurt to talk at the same time as he was making the noise, though, and he flinched. 

“You okay?” Dean asked, evidently feeling Cas jerk.

Cas just murmured noncommittally into his shoulder.

“So, why would your impulses or _whatever’s_ making you do stuff involve me?” Dean asked. His tone was easy, almost joking, but Cas could hear the tension in his voice, feel it in his shoulders. Dean cared about the answer.

“I’m not sure,” Cas said once the ‘purring’ had stopped, “but, I think—I think my instincts are interpreting my emotions for you and viewing you as . . .” he trailed off, fear spiking through him. This could go very bad very fast.

“As?” Dean prompted.

Cas swallowed. “There’s not a perfect word for it in English. The concept is slightly different for angels, who don’t usually have a physical form, the closest I could describe it as would be,” he hesitated for a split second. “My mate.”

Dean went rigid. Cas waited for him to say something, holding his breath, but something happened—his grace twinged; the buzzing changed—and suddenly he was sagging into Dean’s lap, Cas’ head pressed against Dean’s stomach as a string of animal-like noises poured from his throat. Dean said something, but Cas couldn’t understand him, so he just blinked up at his friend with big, blue eyes. His back had started hurting again, dully aching with pain that came in throbs.

Dean was looking down at him, and after a second he smiled a soft, gentle smile, before leaning down and pressing his lips against Cas’.

Cas chirped happily, everything—his mind, his body, his grace, the buzzing—surging in reply. His arms twisted around Dean’s neck, his hand slipping up into his hair as he tasted the mouth that was pressed against his. His mind clicked again and he was thinking normally, but he didn’t stop. Driven by emotions that he’d buried for so long, he deepened the kiss.

Finally Dean broke away, needing air, and even thinking normally Cas keened gently in disappointment and dropped his head onto Dean’s shoulder. Dean was panting slightly, but he pulled Cas closer.

Dean swore, but if Cas was hearing him right it sounded like he was exclaiming in disbelief.

Cas’ stomach pinched and he doubled over, pressing himself into Dean as hunger washed through him. His stomach growled.

Dean snickered. “I know what that sound means, at least. Are you, uh, coherent?”

“Yes.” Cas pulled away, looking at Dean solemnly, but not without a hint of a smile. “I need to eat.”


End file.
